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It's funny that with all the science that has been conducted on sleep, we still don't know why we do it! We know we need it. We know we are better with it than without it. Of course, the best theory out there is that we're recharging our "batteries" for the next day's events.

So what does sleep do in the recharge department? Let's take a look:

Recharge your Body: Deep sleep

We now know that deep sleep (stages three and four) appears to be the most physically restorative sleep. We know that growth hormone is emitted during deep sleep, and that this is the hormone that, among other things, tells tissue to repair itself after a long day of possible damage. In addition, growth hormone tells our bodies how to store fat, and where to put it. Most of your morning energy is dependent upon the amount of deep sleep that you get.

Recharge your brain: REM sleep

Recent research shows that REM sleep is critical for creativity, thought organization, problem solving and memory. It appears that REM sleep may be doing two separate things to our brains. First, it's helping organize our thoughts into a coherent structure, to allow for quick and efficient information retrieval. Next, it may be making neuronal connections stronger for the information we will need, and weaker for that which is more trivial.

Recharging is a process that takes time: Stage one and two sleep

If the only sleep you required was deep sleep (stages three and four) and REM sleep, you might only need about four hours a night. But we all know that with only four hours of sleep you will be pretty tired during the day.

Stages one and two sleep help with the transition times: from wake to sleep (from stage one to two: a brain warm-up for physical and memory restoration); in between deep sleep and REM (a transition from physical restoration to mental restoration); and from sleep back into the waking world (where we lighten up our sleep in order to wake from it!).

While the jury is still out on exactly why we sleep, clearly a recharge is built into this complicated process. And getting the right amount of all of the sleep stages is critical to overall health, wellness and feeling energized the next day.